Tumor progression involves modulation of tumor-cell adhesion during cell migration and degradation of the extracellular matrix (ECM) during tissue invasion. An intricate balance of proteases, their activators and their inhibitors, regulates both these processes during tumor invasion. Three classes of ECM-degrading proteinases are the serine proteinases, metalloproteases and cysteine proteinases. Urokinase plasminogen activator (uPA) initiates a cascade of proteases that can degrade most matrix and basement membrane components and interfere with cell-cell and cell-matrix interactions. uPA, bound to its cell surface receptor, urokinase plasminogen activator receptor (uPAR), is a participant of ECM degradation, as demonstrated by a several-fold increase in plasminogen activation. uPA also activates several growth factors after degradation of ECM components. Binding of uPA with its receptor uPAR activates downstream signaling molecules through a number of pathways, including the mitogen-activated protein kinases (MAPK) and signal transducer and activator of transcription (Stat) pathways.
Recent discovery of RNA interference (RNAi) has opened new avenues in cancer therapy. RNAi is a sequence-specific, post-transcriptional gene-silencing mechanism that is affected through double-stranded RNA molecules homologous to the sequence of the target gene.
RNA interference (RNAi) is a sequence-specific, post-transcriptional gene silencing mechanism, which is triggered by double-stranded RNA (dsRNA) and causes the degradation of mRNA with a sequence homologous to the dsRNA. RNAi depends upon the formation of double-strand RNA (dsRNA) whose antisense strand is complementary to the transcript of a targeted gene. Sequence-specific inhibition RNAi can also be induced in mammalian cells. In one implementation of RNAi, selective degradation of target mRNAs in mammalian cells was achieved by transfection with double-stranded, short interfering RNAs (siRNAs), leading to rapid and efficient degradation of the target. These siRNA were shown to avoid the well-documented, nonspecific effects triggered by longer double-stranded RNAs in mammalian cells.
Prostate cancer is the second most common malignancy in American men, with estimates of 230,110 new cases and approximately 30,000 deaths in 2004. As such, prostate cancer poses a major public health problem in the United States and worldwide. Currently, metastatic prostate cancer is incurable and ultimately claims the life of patients. A factor in the relative seriousness of prostate cancer is the invasiveness of the constituent tumor cells causing metastasis. The invasive nature of tumor cells is a characteristic for cancer metastasis. Tumor cell invasion and metastasis are complex processes with three prominent stages: adhesion of malignant (neoplastic) cells to the extracellular matrix, digestion of the matrix to release cells from the primary tumor mass, and migration of the tumor cells to secondary targets.
Glioblastoma multiforme (GBM) is a highly malignant primary central nervous system neoplasm, which is highly refractory to therapy. One property that makes glioblastoma resistant to treatment is the tendency of the tumor cells to invade normal brain tissue. Therapy which affects normal brain tissue, is not acceptable. Invasiveness is thus considered to be a major determinant of the malignant behavior of human gliomas. Diffuse single-cell invasion, which occurs in all glial tumors regardless of histological grade, is defined as a translocation of neoplastic cells through host cellular and ECM barriers. Malignant gliomas express higher levels of uPA, uPAR and MMP-9 compared with normal brain tissue.
MMPs enhance tumor cell invasion by degrading extracellular matrix proteins, activating signal transduction cascades that promote motility and activating growth factors, such as transforming growth factor β, that are implicated in GBM motility. Expression of the gelatinases MMP-2 and MMP-9 correlates with the invasive and metastatic potentials of various cancers, including gliomas. MMP-9 levels were highly correlated with the histological grade of glioma malignancy. MMP-9 is relevant in endothelial cell morphogenesis and capillary formation in glial/endothelial co-cultures in vitro. MMPs also regulate tumor angiogenesis and might be required for the ‘angiogenic switch’ that occurs during tumor neovascularization.
The proteolytic activity of cathepsin B, a cysteine protease, involves the direct degradation of ECM proteins, including fibronectin, types I and IV collagen and laminin. Cathepsin B also indirectly activates other enzymes involved in the proteolytic cascade that mediates ECM degradation, including metalloproteinases and both soluble and receptor-bound urokinase plasminogen activator (uPA). In addition, cathepsin B has been suggested to increase MMP activity by inactivating tissue inhibitors of matrix metalloproteinases (TIMPs). Cathepsin B, therefore, could be an important upstream regulator in the activation of pro-uPA/plasminogen and pro-MMPs. Cathepsin B has also been shown to contribute to apoptosis by causing cytochrome c release and caspase 9 and 3 activation (key events in the mitochondrial pathway of apoptosis). Increase in cathepsin B expression and reductions in its inhibitor levels were associated with tumor growth, vascularization, invasion and metastasis in various cancers.
siRNA molecules that target a plurality of genes implicated in tumors are desired to develop therapeutic compositions.